Tire treading method and product



Jan. 7, 1941. J. c. Hx-:lNTz l2,228,211

TIRE TREADING METHOD AND PRODUCT Filed April 6, 1958 Patented Jan.- 7, 1941 UNITED v.s'ra'rls PATENT OFFICE y TIRE TREADING METHOD AND rnoDUo'r James C. Heintz, Lakewood, Ohio Application April 193s, serial No. 200,320

Claims.

This invention relates to the retreading of pneumatic tires. Its object is to provide an economical full-circle recapping method and an improved product. More particularly it provides for utilizing worn shoulder portions of the origi- -nal rubber tread in such manner as to afford y much the appearance of a new tire, with the identical side 'conguratiom and providing an antiskid composite wearing surface of old and new rubber, which has the full width of the original tread.

Of the accompanying drawing,

Fig. 1 is a fragmental view illustrating the step of preparing the worn tire tread to receive the new rubber. in a preferred mode oi practicing the invention.

Fig. 2 is a vertical sectional view showing the partly inflated tire with new raw tread rubber thereon, in one form of vulcanizer which may be employed.

Fig. 3 is an enlarged cross-sectional view through the tread region of a tire casing which has been retreaded in accordance with the invention. Fig. 4 is a cross-sectional perspective vie A showing a modied product.

' strip I2 and a rubber tread I3 from which the original anti-skid formation has been worn away to about the contour line A-,-A shown in Fig. 3. The rubber may have been worn away more or les deeply, but even on treads worn smooth or worn entirely through the middle zone of the rubber, there remain considerable depths of shoulder rubber 4Il which retain their original conguration at the Jsides or flanks I5. These original shoulders have a superior adhesion to the carcass which it is diilicult'to reproduce in applying a full retread. after removing all of the old tread rubber;

Fig. 1 illustrates a preferred mode of preparing the worn tread. The tire casing l0, mounted with an inflated air tube upon a suitable rim, is turned slowly against a rapidly rotating rasp wheel I6 which is mounted to receive a radial in-feed, shown by the arrow B, and a" reciprocating arcuate lateral traverse shown by the double-` ended arrow -C. The operator so regulates these feeding actions that the vulcanized tread rubber is channeled or gouged out in a shallow grooved bed I1. 'I'his bed has a convex bottom approxi mately conforming to the transverse curvature of the carcass and deepest in the tread shoulders I4, but terminates short of the edges of said shoulders so as to preserve the remaining full radial tread depth for a substantial width of marginal ground-contacting or sole surface on each side, and leaves a pair of outstanding marginal ribs i8 whose working or wearing surfaces are those of the original worn shoulders.

The next step is to cement the bed I1 and lay thereon, to the necessary depth, vulcanizable raw rubber tread stock I9 which, when cured, becomes an integral resilient rubber tread cap substantially homogeneous with, or of the same v properties as the middle body of the original tread.

The tire`casing, mounted upon a suitable rim and containing the usual inflatable rubber core or curing bag 2l. is` then inserted, inan uninflated condition, in the lower side or half of a suitable tread vulcanizing mold. The diameter and cross-sectional width of the tire are measured after building the raw tread thereon, and a mold having approximately the same diameter of tread cavity is selected. If the uninfiated tire diameter is a little undersize, it is increased in the mold by compressing the tire sides, and if slightly oversize, some'force is used in fitting the tire into the lower half of the mold, before closing the upper half thereon.

The heater part of the vulcanizing apparatus may be of any known or suitable form, the one here illustrated beingl a steam-jacketed structure 22 having a cylindrical backing wall 23 for a pair of rings 24, 25 constituting a molding matrix, preferably segmental, longitudinally divided, made of aluminum and usable with an ordiof the tire is controlled and the rings 24, 25 cen.

tralized between the plates 21./ The molding assembly is clamped together by downward pressure exerted on the upper side plate 21 by a series of the usual clamping screws 29. By reason of the illustrated radial and lateral spacing of the bodies of the rings 21 from the steam jacket and the matrix, providing large ventilation and small heat conduction to said rings, their temperature is maintained well below the vulcanizing point, to prevent overheating of the tire side walls.

'I'he inner molding face of the matrix formed by the rings 24, 25 is transversely concave, and free-edged or without terminal flanges, to seal the tread at its margins and mold a complemental convex wearing face upon the new tread rubber I9, while the tread portion of the carcass II is maintained in substantially its normal transversely convex form. This avoids the creation of cracking strains in the retread, incident to rounding out the tire for service after vulcanizing a tread in flat form onfan underlying con- `cave carcass wall. The absence of lateral confinement at the edges of the tread permits fullwidth treads of various widths to be formed in the same vulcanizer against a matrix wider than the tread, which will generally overhang the edges thereof.

From the inner faces of the matrix rings project suitable intermediate rlbs 30 and outer ribs 3l for molding `complemental longitudinal grooves 3U, 3|EL and adjacent intermediate anti-skid ribs or projections 32 and marginal half-ribs 33 in the new tread. The outer ribs 3l are of a depth permitting the rubber to freely flow under them, in filling out the desired marginal tread contour, and the bottoms of the outermost grooves 3ia formed thereby as shown in Fig. 3 will preferably lie within the contour of the tread surfaces of the rubber ribs I8, or the worn contour line A-A, and in any event are wholly Within the new rubber. The concave marginal faces Sti of the matrix rings, lying laterally outward of the ribsi, act as sealing faces against which thesoles of the ribs I8 are pressed, and as flush molding faces lfor the marginal portions of the new'tread rubber, where it joins the old rubber of said ribs.

In Fig. 2 the full lines represent the approximate shape of the tire when it has been partly iniiated in the mold and its new tread rubber is indented py the ribs of the heated matrix. 'Ihe tire sides are only slightly flattened. The outer portions of the marginaltread ribs I8 are lightly pressed against the molding faces 34, but slight clearances' 35 are present between the inner portions of these ribs and said molding faces. On raising the inflation to the full curing I pressure, which may be around 150 to 200 pounds per square inch, the curing bag and shoulder flank walls of the tire are laterally and radially expanded as shown by the broken lines 36, 31, and the tread margins forced radially outward, slightly beyond their ultimate contour, to eliminate the clearances 35 and completely seal the tread shoulders against substantial lateral flow of the new rubber outwardly beyond the ribs I8, except for such small amounts as may o'verilow into shoulder crevices in some forms of original 'tread patterns. 'I'he vulcanized new rub'- ber tread portion is designated IS. This brings the'joints or seams between new and old rubber at the wearing surface of the tread margins. While the .described method is not wholly limited 'to forming such transversely flush joints, it is aaaaeii become annularly somewhat concave as shown at 38 in Fig. 3.

In the operation of the retreaded tire, before its tread becomes greatly worn, the composite tread shoulders, being relatively lower than in the original tire, are relieved of much or all of the ground pressure at normal load and inflation, while contributing to the lateral support of the middle or working tread zone, but are available for ground support' during fluctuating or steady overloads or underination. A fullwidth rebuilt tread of this contour may be even longer wearing than a new tread under like running conditions, and tread separation or breaking down at the shoulders is much less likely to occur than with full retreads.

In a section of the retreaded tire, the cemented line of junction of old and new rubber, coinciding with the bed I1, is plainly visible, but with proper workmanship, a perfect vulcanized union of the two is obtained. The method is highly economical in the amount of rubber employed, skill in the performance thereof is easily acquired, and the product has practically the appearance of a new tire.

In making the modied product represented in Fig. 4, employing even less new rubber, the step of channeling the old rubber tread is omitted and a bed outlined at IIa prepared on the latf ter by merely buing the worn surface preparatory to cementing for the new tread, or even that roughening may be omitted and the worn surface merely cleaned with a solvent before cementing. The procedure is otherwise as previously described. This view indicates very shallow, closef 1y spaced transverse ribbing 39 molded in the margins of the new rubber and across the joints between it and the old rubber, such as may be impressed by indenting the mold with a knurling tool. The same could be applied to the product of Figs. 2 and 3. In this manner a non-functional, ornamental or identifying marking may be molded upon the tread margins, and because of the concave surfaces 3o upon which these markings are formed, they will last practically until the new tread hasA been again worn down to the first worn contour.

I claim;

l. A retreaded pneumatic tire having a wearing tread of substantially homogeneous resilient rubber composition, with sole surfaces which, as a whole, are transversely convex throughout and laterally limited by abrupt flanking surfaces, comprising new rubber vulcanized between lateral worn shoulders formed by marginal sole portions of the old tread, said new rubber being so disposed With respect to said shoulders that the ground-engaging surface thereof is substantially ush with that of the shoulders adjacent to the points of junction between said new rubber and said shoulders, permitting the original Worn shoulders to act as marginal supporting surfaces when the tread is fully flattened transversely against the ground, the convexity'of the new rubber surface being greater than that of the shoulders.

2. A methodof retreading a. worn pneumatic tire with worn old rubber tread shoulders which comprises channeling out old rubber from between said old'worn tread shoulders applying, in a full circle between said shoulders, vulcanizable rubber of a composition substantially homogeneous with the old rubber, placing the tire, with its tread in transversely convex shape, in a conned position against overlying transversely concave molding and marginal sealing surfaces which cooperate with the sole-surfaces of the shoulders to render the margins ofthe new rubber substantially tlushwith said shoulders, confining the sides of the tire against lateral expansion while permitting' its expansion between the sides and the tread shoulders, applying outward radial pressure to the tire to cause the shoulders to engage said overlying surfaces tightly and substantially prevent lateral flow of the new rubber, and vulcanizing the latter while the tire is so confined at tread and sides.

3. A method according to claim 2 in which, preparatory to applying the new rubber, the old tread rubber is channeled out by removing .a portion thereof, over a width narrower than the tread, to leave outstanding marginal rubber shoulder ribs which act as dams confining the new rubber and becoming vulcanized thereto.

4. A method according to claim 2 in which the old rubber tread surface is left substantially in its transverse worn contour throughout the width of said surface, and the new rubber is ap'- plied over such worn contour prior to vuleanization.

5. The method of retreading a worn pneumatic tire the tread shoulders of which are still laterally limited by abrupt flanking surfaces which comprises channeling out old rubber from between said flanking surfaces around the entire circumference of the tire to leave at least a portion of said iianking surfaces and between them a channel with a convex bottom approximately conforming tothe transverse curvature of the carcass, placing a full circle of vulcanizable tread stock in the channel and vulcanizing said tread stock to the bottom and side walls of the channel.

JAMES C. HEINTZ. 

